Routing Messages via NATS

Since: Dev Builds Only

The functionality described in this section requires a dev build of KumoMTA. You can obtain a dev build by following the instructions in the Installation section.

In addition to local logging and Webhooks, KumoMTA can relay log events (or other queued messages) via NATS JetStream.

KumoMTA supports publishing via NATS, using Lua.

The process to queue log events and make them available for sending via custom_lua as a protocol is covered in the Publishing Log Events Via Webhooks section of the Operations chapter of the User Guide.

Configuring A Queue Handler for NATS

When a message is ready to be queued, the get_queue_config event is fired, at which point we can specify the protocol of the queue, in this case, custom_lua. In the example below, we check whether the message is queued to the nats queue and acts accordingly:

kumo.on('init', function()
  nats = kumo.nats.connect {
    servers = { '127.0.0.1:4222' },
  }
end)

kumo.on('get_queue_config', function(domain, tenant, campaign, routing_domain)
  if domain == 'nats' then
    -- Use the `make.nats` event to handle delivery
    -- of nats log records
    return kumo.make_queue_config {
      protocol = {
        custom_lua = {
          -- this will cause an event called `make.nats` to trigger.
          -- You can pick any name for this event, so long as it doesn't
          -- collide with a pre-defined event, and so long as you bind
          -- to it with a kumo.on call
          constructor = 'make.nats',
        },
      },
    }
  end
  return kumo.make_queue_config {}
end)

Sending Messages via NATS

With the custom_lua protocol defined and a custom event trigger declared, the next step is to catch the make.nats event with code that sends the message contents over HTTP.

The following example publishes the content of the log message via NATS:

-- This is a user-defined event that matches up to the custom_lua
-- constructor used in `get_queue_config` below.
-- The connection must be established before in order to "publish"
-- messages to their destination.
kumo.on('make.nats', function(domain, tenant, campaign)
  nats:publish {
    subject = 'subject',
    payload = message:get_data(),
  }
end)

See the NATS section of the Reference Manual for more information.